The distinguishing features of malignant disease are the capacity of tumors for uncontrolled growth, local invasion of host tissue and dissemination of tumor cells into the circulatory system. The action of proteolytic enzymes has been implicated in many of the events leading to the development of extensive malignant disease. Degradation of connective tissue and basement membrane components are instrumental in the local spread of tumor cells, as well as in their migration into and out of the circulatory system.
Lysosomal enzyme cathepsin B is a thiol proteinase present in most, if not all animal tissues. Thiol proteinase secretions have been seen in primary malignant breast tumors and metastases for patients with previous breast carcinomas. In order to follow-up this possible link between thiol proteinases and cancer activity, assays were developed for thiol proteinases. However, since more than one proteinase can degrade the same synthetic substrate, a less specific demonstration of a particular proteinase is achieved than by immunological methods. Antiserum to the thiol proteinase cathepsin B has been raised but no data was published regarding the specificity of the antiserum. See Barrett, A. J., "Cathepsin B and Other Thiol Proteinases," In Proteinases In Mammalian Cells and Tissues. (1977) In order to be useful as a diagnostic or locational tool, antiserum to cathepsin B must be completely specific as an absolute requirement. An article describing the preparation and characterization of a monospecific antiserum to human cathepsin B was published in 1981, by Poole, Mort and Decker in The Journal of Histochemistry and Cytochemistry, entitled "Immunofluorescent Localization of Cathepsin B and D in Human Fibroblasts," Vol. 29, No. 5, pp. 649-657.